A general portable electronic device with a voice output function, for example, mobile phone, personal data assistant (PDA) and global positioning system (GPS), must use manual way to set a voice volume output. However, a user must use hands to adjust the volume of the portable electronic device once more accompanying the change of background sound volume; the output voice can then be heard clearly under different environments. Thus, it will cause the user to be inconvenient on use.
Thereupon, Taiwan Patent Application No. 93125950 entitled as “Apparatus and method for volume control” mainly discloses generating a corresponding volume adjustment signal and adjusting an output amplitude of an input voice source signal by analyzing the relationship between an environmental interference sound source signal and the input voice source signal when the environmental interference source signal comes in thereby improving inference problems caused from environmental factors to attain to the volume controlling object.
Furthermore, Chinese Patent No. CN1783928 entitled as “Method and apparatus for realizing automatically adjusting volume of ring tone in mobile terminal” mainly discloses setting a corresponding processing program in a cellular phone to automatically realize processing an adjustment to the volume of ring tone depending one a background noise situation of an environment in which it is located to satisfy a cellular phone user with a requirement for a different ring tone volume in a different environment. Therefore, a user's cellular phone can automatically detect the background noise situation of the current environment and process the automatic adjustment of the ring tone volume of the cellular phone depending on the aforesaid background noise situation so as to exempt the cellular phone user from a tedious operation of the manual ring tone volume adjustment thereby being convenient for the user's use.
Moreover, U.S. Pat. No. 6,298,247 entitled as “Method and Apparatus for Automatic Volume Control” is mainly applied on a communication device; it can measure background noise, and automatically adjust a volume of an output signal depending on the measured background noise signal.
The conventional technologies mentioned above disclose the technologies of automatically adjusting the output volume. The disclosed technologies are all used for adjusting the voice amplitude, i.e. so-called volume part. However, under certain environments, because background noise is too loud, it is unable to hear the output voice signals clearly even if the volume is adjusted to the largest. Besides, that the voice amplitude is adjusted higher causes the use of a speaker to be shortened. Therefore, how to effectively improve the problems of traditional automatic voice adjusting technologies is a topic to be solved urgently.